Debate about older adults' driving skills often touches on obvious impairments, such as failing vision and heavy medication use. But a new study suggests a deeper neurological explanation for why seniors have a hard time spotting obvious objects on the road: They might actually just be better at perceiving large-scale movement in the background, an ability that could compete with attention paid to smaller objects in the foreground.

"The amount of visual information around us is huge, and we don't have the brain power to process it all," Duje Tadin, of University of Rochester's Department of Brain and Cognitive Sciences, said in a prepared statement. So, to prioritize, the brain uses "spatial suppression" to filter out what it deems less relevant visual information, which is often that coming from the background.

Tadin and his colleagues hypothesized that this spatial suppression was being mediated at least in part by the middle temporal visual area and so by turning down this area's function—as might happen in older adults—they could also reduce spatial suppression. The results were published online January 25 in The Journal of Neuroscience.

The research team used transcranial magnetic stimulation to send mild electrical current to the middle temporal visual area of the cortex. After 15 minutes of the 1 Hz stimulation to the noggins of six young healthy volunteers, the researchers found that the subjects were much more attuned to broader movements in the background than they had previously been. "Disruption of [the middle temporal visual area] improved motion discrimination of large, moving stimuli," the researchers wrote in their paper.

The tamping down of the middle temporal visual area did not, however, seem to affect perception of small foreground objects' movement. Thus, with the brain receiving even more visual data, it might become less efficient at focusing on the important stuff—such as a person dashing across the road.

The findings also might have implications for populations other than the elderly, including people with schizophrenia or depression. "These paradoxical results mimic special population findings," the researchers noted. "Particularly patients with a history of depression who exhibit better-than-normal motion perception of large patterns coupled with normal perception of small, moving stimuli." By better understanding what parts of the brain might be contributing to altered visual processing, researchers might some day be able to develop improved disease models and possibly even treatments.

Image courtesy of iStockphoto/CWImages

The views expressed are those of the author and are not necessarily those of Scientific American.

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